a. Field of the Invention
The invention relates to a backlight module in general and more specifically to a backlight module using a polarized light source.
b. Description of the Related Art
FIG. 5 shows a schematic diagram of a conventional edge-lighting type backlight module. Referring to FIG. 5, in a backlight module 100, a light source 102 is disposed adjacent to a side surface 104c of a light guide plate 104, and a light beam emitted by the light source 102 enters the light guide plate 104 and is deflected by micro dots 106 spread on a bottom surface 104b of the light guide plate 104. The micro dots 106 may destroy the condition of total internal reflection to allow the light beam to leave the light guide plate 104 via the light-emitting surface 104a. Commonly, the light source 102 may include at least one light-emitting diode. Since the current trend is towards an even brighter light-emitting diode, the number of light-emitting diodes used in the backlight module 100 is reduced. In that case, bright and dark regions in sharp contrast are liable to be formed to adversely affect image display as a light-mixing distance for light-emitting diodes is not sufficient. Further, since there is uneven distribution of the quality of light-emitting diodes with mass production, a light emitting diode with poor quality may, after being used for some time, break down first to result in apparent dark regions formed in front of the damaged light emitting diode to adversely affect image display.
Taiwan patent publication no. 200935630 discloses a light-emitting device using a polarized light-emitting diode as a light source, and a die of the light-emitting diode includes a polarizing layer, a light-blocking layer, and a reflective layer. Taiwan patent publication no. 200919025 discloses an optical film set including a diffusion film, a prism sheet, a reverse prism sheet, a brightness enhancement film, a non-multilayer reflective polarizer or a combination of at least two of them. The optical film set is disposed on a light guide plate. U.S. Pat. No. 7,796,212 discloses a liquid crystal display having a light source, a polarized light guide plate, a liquid crystal panel, and a diffusion film. The polarized light guide plate is allowed to polarize a light beam emitted by the light source. U.S. patent publication no. 20060091412 discloses a light-emitting diode package having a light-emitting diode chip and a light source, and the light source may emit a p-polarized light beam and an s-polarized light beam. However, the above conventional designs all suffer problems of insufficient light-mixing distances and dark regions as a result of a damaged light source.